This invention relates to a switching regulator which is coupled to a horizontal deflection circuit in a manner which provides the deflection circuit with regulated supply voltage and additionally improves the regulation of an ultor voltage produced from the retrace pulses.
Increasing emphasis on reduced power consumption has led to the increased use of switching regulators for powering television receivers. In switching regulators, a switch coupled to the raw or unregulated direct voltage supply is periodically turned on and off with a duty cycle adapted to regulate the controlled voltage. A major load on such regulators in a television receiver is the horizontal deflection circuit and the associated kinescope ultor voltage generator. Switching regulators are normally configured in a feedback arrangement by which variations in the voltage or current at a particular point in the circuit can be reduced, i.e., regulated. If the voltage applied as supply to the horizontal deflection circuit is regulated, the voltage across the deflection switching transistor will be controlled, but the regulation of the ultor supply is then completely dependent upon the effective impedances of the high-voltage transformer, rectifiers and associated filter capacitors. On the other hand, if a voltage representative of the ultor voltage is regulated, the impedance of the ultor generator is reduced by the loop gain of the feedback regulator, but the supply voltage applied to the horizontal deflection circuit and the resulting retrace voltage pulse amplitude across the deflection switch are variable. Consequently, the horizontal deflection switch must have a higher voltage rating.
U.S. patent application Ser. No. 875,530 filed Feb. 6, 1978 in the name of Peer et al. describes a switching regulator in which an SCR is used as the control element for controllably charging a capacitor from the unregulated supply through the series connection of an inductor and a winding coupled to the horizontal deflection circuit. In the Peer et al. arrangement, the inductor must be small enough so that the current in the inductor and SCR can be reduced to zero during the retrace interval by the difference between the unregulated direct voltage and the sum of the turn-off voltage pulse generated across the winding and the regulated voltage. As a result, relatively large peak currents may flow in the inductor and in the storage capacitor during the capacitor charging interval. These relatively large currents undesirably result in relatively large I.sup.2 R or heating losses. The SCR turn-off requirements and the relatively large variations in regulator current with changes in load current such as those resulting from kinescope beam current changes vary the regulator peak current. Due to the coupling between the turn-off winding and the horizontal deflection circuit, the varying regulator current tends to reduce the retrace time with increases in beam current, thereby increasing the peak retrace voltage in a manner tending to compensate for the reduction in ultor voltage due to kinescope beam current loading.
A flywheel diode when used with the arrangement of Peer et al. allows the SCR to be turned off by the turn-off winding independent of the filter inductor, whereby the filter inductor may be increased in size to reduce the peak filter capacitor charging currents and therefore reduce heating losses, while guaranteeing SCR turn-off during the retrace interval. With such an arrangement, however, the advantageous compensation of the retrace pulse amplitude in the presence of kinescope beam loading is not available.